Process for preparing photographic negatives



.which represent the printing areas of the plate.

United States Patent Q r 3,072,496 PROCESS FOR PREPARING PHOTOGRAPHICNEGATIVES Bernard Robert Halpern, Swarthmore, Pa., assignor to E. I. duPont de Nemours and Company, Wilmington, Del., a corporation of DelawareNo Drawing. Filed Feb. 18, 1960, Ser. No. 9,444 7 Claims. (Cl. 117-5.5)

This invention relate to the graphic arts field and more particularly itrelates to photomechanical processes in the graphic arts field. Stillmore particularly it relates to improvements in processes for producingphotographic printing negatives for use in making photomechanicalprinting plates.

It is old in the art to make duplicate printing plates for any method ofprinting by photographing a reproduction proof pulled from a type form,or by photographing a prepared form directly so as to obtain a negativethat can be used to make a photomechanical plate. These negatives,commonly referred to as line negatives, are placed in contact with aplate coated with a light-sensitive emulsion. Exposure of the plate to alight source through the negative insolubilizes the exposed areas toprovide a resist for etching or for chemical differentiation, that afterappropriate processing, results in a printing plate that is suitable fora printing process such as letterpress, gravure, or offset lithography.The above methods require exacting preparation of the printing forms forpulling a satisfactory proof, and precise process cameras fortransmitting all of the character detail to thenegative. Since the bulkof all text composition is currently cast on type composing machines, itis necessary to convert this composition into a suitable negative orpositive before the text can be used on a photomechanical plate. Thistransparency can then be used to prepare any number of duplicate platesas may be needed.

A simplified and more direct method for producing a negative from anexisting printing form for use in photomechanical platemaking, is topull an impression directly on a film coated with a photographicgelatino-silver halide emulsion. When this is done, using anyconventional hydrophobic printing ink, a resist is formed which preventsthe action of processing solutions in those areas In the case ofgelatino-silver halide emulsion layers, photographic developers willdevelop silver in the non-printing areas, assuming,.of course that theoperation is done under normal room lighting, which, in effect, flashexposes the silver halide layer. By dissolving, wiping away, orotherwise (i.e., surface tension reduction with wetting agents to permitpenetration) removing the inked impression and then fixing out the filmwith a conventional photographic fixer, the silver halide which wasprotected by the ink during development is removed to give clear areas,and the film becomes, in effect, an accurate photographic negative ofthe printing plate. The inked impressions may be made in anyconventional proof press, in the manner known to those skilled in theart. No camera or dark room equipment is necessary with this lattermethod and the films are normally handled under ordinary room lightingconditions. In the case of lightsensitive gelatino-silve-r halideemulsion coated film, the

latter must be exposed to light so that black silver will be developedexcept where the printed impression covered 3,072,496 Patented Jan. 8,1963 by the ink prevents the developer from acting to reduce the silverhalide to silver. The ink, after development, is removed by a suitablesolvent and the film is then immersed in a fixing composition whichdissolves the silver halide, which has not been acted on by thedeveloper and forms clear areas which gives a negative of the printedimpression. It will be evident that because light is not involved in theactual making of the image, inks or other pigmented compounds need notnecessarily be used. Any suitable composition which will resist theaction of the processing compositions may be used. It is also evidentthat a positive can be produced by making a print resist and thenfixing, removing the ink resist and then developing. In this case theprinted impression will be developed to black silver and the unprintedareas will be clear thus forming a positive of the printed material. Itis with this method of inking directly on a gelatino-silver halide layerthat the present invention is concerned.

Although the above method ofinking directly on a gelatino-silver halidelayer eliminates the necessity of using cumbersome proces cameras andprocessing the exposed film under photographic dark-room conditions, thesystem has some serious drawbacks which become particularly evident whenused in conjunction with the newer printing plates now commerciallyavailable. In place of the usual metal plates sensitized withbichromated gelatin, the new plates are composed of photopolymerizablelayers such as those described and claimed in Plambeck US. Patent2,791,504 and Martin et al., US. Serial No. 596,766, filed July 7, 1956,now US. Patent 2,927,022, issued March 1, 1960. Printing plates composedof the said photopolymerizable layers are easy to make and morefaithfully reproduce the subject matter to be printed from the negativeto which the plate is photographically exposed than the plates of theprior art. The outstanding difficulties encountered in making negativesby inking directly'on the gelatino-silver halide layers are two-fold.Ink squeezeout is one of the difli culties which results in loss offidelity and grayed impression areas during the printing of the proofand also the tendency of characters to be slightly bolder with mottledcenters than in the original. Wherever large quantities of paper areused, as is the case in commercial printing plants, the atmospherenearly always contains substantial amounts of lint and dust. This causesdiscontinuous inked images because the particles in the air will mixwith the ink on the form rollers of the press and also settle onsurfaces and prevent satisfactory ink transfer. When films containingsuch images are processed,

a poor negative results. An exposed printing plate from high-qualitynegatives from relief printing forms. A further object is to providesuch a process which overcomes the deficiencies of prior art proceduresdue to lint and dust particles. A still further object is to providesuch a process which eliminates the undesirable effects of inksqueezeout. Still further advantages will appear hereinafter.

These and other objects are realized by the instant invention whichconsists in a process for preparing highquality negatives from a reliefprinting form, e.g., line, halftone or combined line and halftone plateor type form, which comprises lightly coating the relief surface of saidform with a hydrophobic developer resist, pulling a first pro-of on theemulsion surface of a flexible, transparent film coated with alight-sensitive photographic emulsion layer, cleaning said reliefsurface of said form to remove any remaining developer resist, againlightly coating said relief surface with said developer resist andpulling a second proof on said film in exact register with said firstproof, developing said emulsion layer in areas not coated with saiddeveloper resist and subsequently removing said developer resist and thephotographic emulsion layer thereunder from said film.

High-quality negatives can be produced by the above process to take fulladvantage of the new polymeric printing plates referred to above. Theinvention resides in the novel process of inking which will behereinafter more fully described. It comprises first lightly inking theplate or type form to be duplicated by the usual proof press and thenpulling a proof on a photographic emulsion coated film by making animpression on the film thin enough so that the tendency for inksqueezeout is minimized. The printing plate is then wiped or washed freeof its remaining ink coating. The plate is then lightly re-inked and asecond impression is made on the film in exact register with the firstimpression. The intermediate step of washing the plate and second inkingserve to shift the location of defects caused by dust and lint specks onthe printing form so that in two or more inkings a continuous film ofink duplicating the printing surface is produced as a developer resiston the gelatino-silver halide layer of the film. By this method largereverses and solids as well as text and half-tones are converted withgood quality. Any type of gelatino-silver halide emulsion may be used,including high-contrast negative materials and direct positive films.The latter films have been found to be particularly suitable as they areless sensitive to prolonged handling in the proof press room. Chemicalblackeners, such as sodium sulfide, can be used instead of developersthus eliminating the need for the fogging exposure to light. Normal roomlighting i satisfactory although high intensity fluorescent lights andmercury lamps should not be in use during the proofing operation,particularly in the case of high speed and direct positive emulsionsbecause of the formation of photolytic sliver which is independent ofthe developing process.

The type of ink used is generally only a matter of personal choice,since any hydrophobic ink which will transfer satisfactorily from theprinting form to the gelatinosilver halide coated film to form adeveloper resist will be suitable. Many suitable lithographic inks arecommercially available. A suitable ink may also be prepared by meltingtogether parts of petroleum jelly, /2 part of amorphous silica and Apart of carbon black. Inks need not necessarily be used as a processingsolution resist and can incorporate photographic desensitizers whichwill act directly on the emulsion to prevent development of the imageareas. Resists can also be prepared without inclusion of a pigment ordesensitizer such as by melting together one part of beeswax and onepart petroleum jelly.

The processing solutions, namely alkaline photographic developers andacid photographic fixers may be of the conventional type and are sochosen as to be the most elficacious for the particular gelatino-silverhalide emulsion used.

The invention will now be illustrated in and by the following examples:

4 Example I A printing form of good quality was locked in a proof presscapable of printing exact dot on dot register. After the normalmake-ready and test proofs, a photographic direct positive clear filmwas secured to the proof press cylinder. A thin ink application is thenprinted on the emulsion side of the film. The printing form was thenwiped clean with a solvent for the ink applied sparingly to a lint-freerag and the form then re-inked. A second thin ink application wasprinted in exact register over the first impression. The film elementwas then placed, emulsion side up, in a tray containing a developerhaving the following composition:

Water liter 1 Sodium sulfite (anhy.) ..grams 120.0 Paraformaldehyde do30.0 Potassium metabisulfite do 150.0 Boric acid, crystals do 30.0Hydroquinone do 90.0 Potassium bromide do 6.0 Water to make 2 liters.

The tray was rocked for about 45 seconds to uniformly develop the filmand provide a maximum density of at least 3.5. The film was thentransferred to a tray containing an acid short stop bath composed of 5%acetic acid and agitated for about five seconds. After this treatment, acotton wad which was dampened with 50-50 ethyl alcohol and hypo fixingbath solution was used to wipe off the ink. Care was taken to remove allof the ink by turning the cotton and rewiping. The film was thentransferred to a tray containing a fixing bath having the followingcomposition:

Water (15 C.) ml 600.0 Sodium thiosulfate (anhy.) ..grams 15.0 Sodiumsulfite (anhy.) do 18.0 Potassium alum do 20.0 Acetic acid (glacial) ml12.0

Water to make 1.0 liter.

The film was agitated in the above bath for about one minute or untilthe area which had been covered by the ink was clear. The film was thenwashed and dried by conventional methods. The negative obtained was anexcellent reproduction of the original printing form. The negative wasplaced over a photopolymerizable printing element prepared as describedin Example IV of Martin et al., U.S. Serial No. 596,766, filed July 9,1956, now U.S. Patent 2,927,022; and Example 3 of Burg, U.S. Serial No.750,868, filed July 25, 1958. The element and negative were placed in avacuum frame and exposed to 1.75 watts of actinic radiation per squareinch for 12 seconds from an l800-watt, high-pressure, mercury-arc lamp.After exposure, the unexposed areas of the element were removed by spraywashing for 8 minutes using an 0.08 N aqueous solution of sodiumhydroxide. A sharp, polymerized relief printing plate was obtained, therelief areas corresponding to the clear areas and relief or printingareas of the original plate. The resulting plate, when used in aconventional printing press, gave reproductions of good qualitycomparable to those obtained from the original printing form. There wereno pinhole or other defects discernible in the text, half-tone or solidareas of the image as is so often the case where a single inking processis used. Naturally, any gross surface defects such as pits, batters, orgouges in the printing surface will be reproduced. During the making ofthe above negative, a control negative was made under the sameconditions except that only a single normally inked impression was madeon the proof press. All other conditions were the same. Aphotopolymerization printing plate exposed to the resulting processednegative printed larger and more Example II Example I was repeated usingin place of the direct positive film, a high contrast gelatino-silverchlorobromide film. After inking in the manner described in Example Ithe film element was placed emulsion side up, in a tray containing adeveloper having the following composition:

Water ml 500 Methyl-p-aminophenol grams 3.0 Sodium sulfite (anhy.) do45.0 Hydroquinone do 12.0 Sodium carbonate (anhy.) do 67.5 Potassiumbromide do 1.9

Water to make 2.0 liters.

The tray was rocked for about 20 seconds to uniformly develop the filmand provide a maximum density of at least 3.5. The processing of thefilm was then continued as described in Example I including the removalof the ink, fixing, washing, drying and exposure steps. The polymerizedrelief printing plate had characteristics similar to those of a plateexposed through the negative formed using the direct positive clearfilm.

An important aspect of the invention is that any film having a coatingof a gelatino-silver halide emulsion may be used in the process. Forexample, high-contrast films which are suitable for graphic arts workmay be used. As indicated above, where high speed and/or very sensitivefilms are used, subdued room lighting is desirable to reduce thepossibility of producing photolytic silver which would be formed in thelayer in the areas which would be eventually covered by the ink when animpression is pulled. During the fixing operation after the ink isremoved, such spontaneously formed silver would remain and could not beremoved by the fixing solution. This would, of course, prevent printinga clear image unmarred by defects of the negative onto thephotopolymerizable printing plate. The emulsion layer to receive the inkimpression need not necessarily have a transparent film support. Atranslucent support may be used and may have auxiliary layers inaddition to the emulsion layer to provide such translucency. Theemulsion layer itself may contain delustering agents which provides amatted surface which can aid in preventing ink squeezeout. It also aidsin allowing trapped air to escape to provide rapid contact between thenegative and the plate when printing down in vacuum printing frames.

Any relief, intaglio, or planographic printing surface may be used asthe printing form for taking the impression. For example, slugcomposition (Linotype and Intertype), individual type (Monotype andfoundry type), photoengravings and duplicate plate (electrotypes) andlithographic printing plates may be used. The printing can be made fromprinting plates composed of zinc, copper, aluminum, magnesium,,steel,nickel, chromium, brass, type metal, plastic, etc.

It will be appreciated that many variations can be taken advantage ofusing the negatives of the novel process of the invention. For example,either right-reading or wrong-reading printing plates may be made byeither exposing the photopolymer plate through the emulsion side orthrough the non-emulsion side of the processed negative film.

When it is desired to make gravure plates, for example, the inked filmmay be processed by first fixing and then, after washing, and removingthe ink, developing the emulsion which was covered by the ink. In thiscase the area covered by the ink will become the image and a r 6transparent positive will result. Upon printing a suitable plate fromthis film one can obtain a gravure plate wherein the printing areas willbe depressed and non-printing areas will be raised.

The film support for the emulsion layers used in the novel process maybe any suitable transparent plastic. For example, the cellulosicsupports, e.g., cellulose acetate, cellulose triacetate, cellulose mixedesters, etc. may be used. Polymerized vinyl compounds, e.g.,copolymerized vinyl acetate and vinyl chloride, polystyrene, andpolymerized acrylates may also be mentioned. An important aspect whichgoverns the selection of the proper support is dimensional stabilitybecause of necessity of exact register both in the inking operation andthe printing operation. The film formed from the polyesterificationproduct of a dicarboxylic acid and a dihydric alcohol made according tothe teachings of Alles, US. Patent 2,779,684 and the patents referred toin the specification of that patent. Other suitable supports are thepolyethylene terephthalate/isophthalates of British Patent 766,290 andCanadian Patent 562,672 and those obtainable by condensing terephthalicacid and dimethyl terephthalate with propylene glycol, diethyleneglycol, tetramethylene glycol or cyclohexane 1,4-dimethanol(hexahydro-p-xylene alcohol). The above polyester films are particularlysuitable because of their dimensional stability.

It will be evident that the double inking process can also be applied tonon-photographic, but chemicallysensitized films which, by being broughtinto contact with a suitable reagent, form image transparencie which maybe used to expose the above-described printing plates.

The main advantage of the novel process of the invention is that itovercomes the loss of fine detail and the mottling due to incompleteinking which is the inherent deficiency of the prior art processes.

What i claimed is: V

1. A process for preparing high-quality photographic negatives from arelief printing form which comprises lightly coating the relief surfaceof said form with a thin layer of a hydrophobic developer resist,pulling a first proof on the emulsion surface of a flexible, transparentfilm coated with a light-sensitive photographic emulsion layer, cleaningsaid relief surface of said form to remove any remaining developerresist, again lightly coating said relief surface with a thin layer ofsaid developer resist and pulling a second proof on said film in exactregister with said first proof, developing said emulsion layer in areasnot coated with said developer resist and subsequently removing saiddeveloper resist and the photographic emulsion layer thereunder fromsaid film.

2. Process according to claim 1 wherein said developer resist is ahydrophobic ink.

3. Process according to claim 1 wherein said photographic film is ahigh-contrast gelatino-silver chlorobromide film.

4. Process according to claim 1 wherein said light- 'sensitivephotographic emulsion is a direct positive type emulsion.

5. Process according to claim 4 wherein said developer resist is ahydrophobic ink.

6. Process according to claim 4 wherein said photographic film is ahigh-contrast gelatino-silver chlorobromide film.

7. A process for preparing high-quality photographic right-readingnegatives from a relief printing form which comprises lightly coatingthe relief surface of said form with a thin layer of a hydrophobicdeveloper resist, pulling a first proof on the emulsion surface of aflexible, transparent film coated with a light-sensitive photographicemulsion layer, cleaning said relief surface of said form to remove anyremaining developer resist, again lightly coating said relief surfacewith a thin layer of said developer resist and pulling a second proof onsaid film in exact register with said first proof, removing saidemulsion from said film in areas not covered by said developer resist,removing only said developer resist from said film, and developing saidphotographic emulsion on said film previously coated by said developerresist.

References Cited in the file of this patent UNITED STATES PATENTS117,376 Brandon July 25, 1871 8 Eader May 12, 1936 Boni Feb. 7, 1956M011 et al Feb. 14, 1956 OTHER REFERENCES

1. A PROCESS FOR PREPARING HIGH-QUALITY PHOTOGRAPHIC NEGATIVES FROM ARELIEF PRINTING FORM WHICH COMPRISES LIGHTLY COATING THE RELIEF SURFACEOF SAID FORM WITH A THIN LAYER OF A HYDROPHOBIC DEVELOPER RESIST,PULLING A FIRST PROOF ON THE EMULSION SURRFACE OF A FLEXIBLE,TRANSPARENT FILM COATED WITH A LIGHT-SENSITIVE PHOTOGRAPHIC EMULSIONLAYER, CLEANING SAID RELIEF SURFACE OF SAID FORM TO REMOVE ANY REMAININGDEVELOPER RESIST, AGAIN LIGHTLY COATING SAID RELIEF SURFACE WITH A THINLAYER OF SAID DEVELOPER RESIST AND PULLING A SECOND PROOF ON SAID FILMIN EXACT REGISTER WITH SAID FIRST PROOF, DEVELOPING SAID EMULSION LAYERIN AREAS NOT COATED WITH SAID DEVELOPER RESIST AND SUBSEQUENTLY REMOVINGSAID DEVELOPER RESIST AND THE PHOTOGRAPHIC EMULSION LAYER THEREUNDERFROM SAID FILM.